The external acoustic meatus (ear canal) 10 is generally narrow and contoured, as shown in the coronal view illustrated in FIG. 1. The adult ear canal 10 is axially approximately 25 mm in length from the canal aperture 12 to the tympanic membrane or eardrum 14. The lateral part of the ear canal 10, i.e., the part away from the tympanic membrane, is the cartilaginous region 16. The cartilaginous region 16 is relatively soft due to the underlying cartilaginous tissue, and deforms and moves in response to the mandibular or jaw motions, which occur during talking, yawning, eating, etc. The medial part of the ear canal 10, i.e., the part toward the tympanic membrane 14, is the bony region 18 (or “bony canal”). The bony region 18, which is proximal to the tympanic membrane 14, is rigid, roughly 15 mm long and represents approximately 60% of the canal length. The skin in the bony region 18 is thin relative to the skin in the cartilaginous region and is typically more sensitive to touch or pressure. There is a characteristic bend, which occurs approximately at the bony-cartilaginous junction 20, that separates the cartilaginous region 16 and the bony region 18, commonly referred to as the second bend of the ear canal.
Debris 22 and hair 24 in the ear canal are primarily present in the cartilaginous region 16. Physiologic debris includes cerumen or earwax, sweat, decayed hair and skin, and sebaceous secretions produced by the glands underneath the skin in the cartilaginous region. Non-physiologic debris is also present and may consist of environmental particles, including hygienic and cosmetic products that may have entered the ear canal. The bony portion of the ear canal does not contain hair follicles, sebaceous, sweat, or cerumen glands. Canal debris is naturally extruded to the outside of the ear by the process of lateral epithelial cell migration, offering a natural self-cleansing mechanism for the ear.
The ear canal 10 terminates medially with the tympanic membrane 14. Lateral of and external to the ear canal is the concha cavity 26 and the auricle 28, which is cartilaginous. The junction between the concha cavity 26 and cartilaginous region 16 of the ear canal at the aperture 12 is also defined by a characteristic bend 30, which is known as the first bend of the ear canal. Canal shape and dimensions can vary significantly among individuals.
As discussed in U.S. Pat. No. 6,940,988 to Shennib et al. (“Shennib et al.”), conventional hearing devices that fit in the ear of individuals generally fall into one of 4 categories as classified by the hearing aid industry: (1) the Behind-The-Ear (BTE) type which, as the designation indicates, is worn behind the ear and is attached to an ear mold which fit mostly in the concha; (2) the In-The-Ear (ITE) type which fits largely in the auricle and concha areas, extending minimally into the ear canal; (3) the In-The-canal (ITC) type which fits largely in the concha area and extends into the ear canal (see, e.g., Valente M., Strategies for Selecting and Verifying Hearing Aid Fittings, Thieme Medical Publishing, pp. 255-256, 1994), and (4) the Completely-In-the-Canal (CIC) type which fits completely within the ear canal past the aperture (see, e.g., Chasin, M. CIC Handbook, Singular Publishing, p. 5).
Extended wear hearing devices are configured to be worn continuously, from several weeks to several months, inside the ear canal. Such devices may be miniature in size in order to fit entirely within the ear canal and are configured such that the receiver (or “speaker”) fits deeply in the ear canal in proximity to the tympanic membrane 14. To that end, receivers and microphones that are highly miniaturized, but sufficiently sized to produce acceptable sound quality, are available for use is hearing devices. The in-the-canal receivers are generally in the shape of a rectangular prism, and have lengths in the range of 5-7 mm and girths of 2-3 mm at the narrowest dimension. Receivers with smaller dimensions are possible to manufacture, but would have lower output efficiencies and the usual challenges of micro-manufacture, especially in the coils of the electromagnetic transduction mechanism. The reduction in output efficiency may be unacceptable, in the extended wear hearing device context, because it necessitates significant increases in power consumption to produce the required amplification level for a hearing impaired individual. Examples of miniature hearing aid receivers include the FH and FK series receivers from Knowles Electronics and the 2600 series from Sonion (Denmark). With respect to microphones, the microphones employed in in-the-canal hearing devices are generally in the shape of a rectangular prism or a cylinder, and range from 2.5-5.0 mm in length and 1.3 to 2.6 mm in the narrowest dimension. Examples of miniature microphones include the FG and TO series from Knowles Electronics, the 6000 series from Sonion, and the 151 series from Tibbetts Industries. Other suitable microphones include silicon microphones (which are not yet widely used in hearing aids due to their suboptimal noise performance per unit area).
Recently introduced extended wear hearing devices are configured to be located in both the cartilaginous region 16 and the bony region 18 of the ear canal 10. A design exists for an extended wear hearing device intended to rest entirely within the bony region 18 and is disclosed in U.S. Patent Pub. No. 2009/0074220 to Shennib (“Shennib”). There are a number of advantages associated with the placement of a hearing device entirely within the ear canal bony region 18. For example, placement within the ear canal bony region 18 and entirely past the bony-cartilaginous junction 20 avoids the dynamic mechanics of the cartilagenous region 16, where mandibular motion, changes in the position of the pina, such as during sleep, and other movements result in significant ear canal motion that can lead to discomfort, abrasions, and/or migration of the hearing device. Another benefit of placement within the ear canal bony region 18 relates to the fact that sweat and cerumen are produced lateral to the bony-cartilaginous junction 20. Thus, placement within the bony region 18 reduces the likelihood of hearing device contamination. Sound quality is improved because “occlusion,” which is caused by the reverberation of sound in the cartilaginous region 16, is eliminated. Sound quality is also improved because the microphone is placed relatively close to the tympanic membrane, taking advantage of the directionality and frequency shaping provided by the outer parts of the ear, so that sound presented to the hearing device microphone more closely matches the sound that the patient is accustomed to receiving at their tympanic membrane.
Operating close to the tympanic membrane allows the hearing instrument to generate a higher sound level while using less power than if the hearing aid were operated at a more distant location from the tympanic membrane. As discussed in Shennib et al., the efficiency of a hearing device is generally inversely proportional to the distance or residual volume between the receiver (speaker) end and the tympanic membrane, the closer the receiver is to the tympanic membrane, the less air mass there is to vibrate, and thus, less energy is required.
In relation to in-the-canal hearing devices, for example, as noted in U.S. application Ser. No. 13/303,406, the configuration of conventional hearing device batteries prevents batteries that have sufficient power capacity (measured in, for example, milliamp hours (mAh)) from being shaped in a manner that would enable an overall hearing device configuration which allows the hearing device to fit within the ear canal bony region in a significant portion of the adult population.
Thus, it would be helpful to be able to reduce the current/power consumption of a hearing device.
It would be helpful to be able to reduce the current/power consumption of a deep in the canal hearing device that includes a battery (power source) constituted of a single battery or a single cell battery. In relation to providing a deep canal extended wear hearing aid, for example, preferably all four of the following operational/performance criteria are satisfied.                1. Current Consumption: The hearing aid must consume a quantity of current commensurate with state of the art batteries, constrained by a volume equal to the available volume in a patient's ear canal, such that a “non-rechargeable” single battery or a single cell battery, provides an operating lifetime that meets or exceeds a minimum specified duration (amount of time). By way of example, for a 3 month lifetime, this current is less than 30 μA.        2. Compression Range: The hearing aid must amplify “quiet sounds” with a high gain on the order of 40 dB, while amplifying “loud sounds” with a small gain, or no gain at all. A “quiet sound” is defined as a sound on the order of 40 dB relative to 20 μPa, while a “loud sound” is defined as a sound on the order of 100 dB relative to 20 μPa. The required compression range is then 40 dB, adjusting the gain from a maximum of 40 dB in quiet environments to a minimum of 0 dB in loud environments.        3. Noise: The hearing aid must not add significant random noise to the amplified signal. To satisfy this requirement, an input referred integrated noise signal should be less than 30 dB relative to 20 μPa integrated from 200 Hz to 5 kHz.        4. Distortion: Low distortion is required, which is defined as less than 5% total harmonic distortion for both loud and quiet input signals as defined above.        
It would be helpful to be able to reduce the current/power consumption of a hearing device that includes a rechargeable battery and/or increase the acoustical pressure generated by such a device.
It would be helpful to be able to improve one or more aspects of hearing device sound quality.